The objective of the research project is to attempt to clarify the factors inducing an enlargement of adipose tissue by adipocyte multiplication and to examine adipose tissue of obese, diabetic man. Recently methods have been developed to isolate, characterize and quantitate cells in adipose tissue developing into adipocytes. This has been possible by labelling these cells in vivo, purifying them by different procedures, followed by culture in a substrate rich medium. Quantitation is obtained by culture in media preventing multiplication. The cells develop into adipocytes of characteristic morphology and function, and the conversion can be manipulated in vitro and in vivo. In the project the cells will be further characterized during their development. Effects in vitro of different agents on multiplication, determination and expression of these precursor cells to adipocytes will be examined in the rat by following DNA-formation per unit time (multiplication), the number of adipocytes formed (determination) and the rate of their formation (expression). These agents include substrate and hormones, adipose tissue and fractions thereof, and substances interfering with lipoprotein lipase activity and with cyclic nucleotide concentration. Effects in vivo of age, feeding, obesity, diabetes and hormones will be examined in rats and man in terms of formation of adipocytes and preadipocytes as well as influence on the conversion of the precursor cells to adipocytes. Finally, another fraction of cells obtained during preparation of fat tissues, probably containing endothelial cells, will be further characterized.